Electrical switch construction and end plug therefor or the like

ABSTRACT

An end plug for a switch construction, the plug having two identical inward and outward extensions extending from a large central portion so as to be usable in a like manner regardless of which extension is the inward or outward thereof in its assembled relation with the switch casing whereby the inward extension is adapted to provide a locating means for a spring inside the switch casing and the outward extension is adapted to provide means for spacing an exposed part of one of the switch conductors from the casing a predetermined distance. Each of the extensions of the plug has an axial length at least approximately the same as the axial length of the central portion thereof. Each of the extensions of the plug of one embodiment has a locating means intermediate its ends whereby the locating means on the inward extension is adapted to provide locating means for positioning one end of the internal spring in the switch casing and the locating means on the outward extension is adapted to provide means for mechanically locking an adhesive thereto that secures the casing to the exposed portion of the conductor whereas in another embodiment each of the extensions of the plug has a smooth frusto-conical configuration.

United States Patent Merrill ELECTRICAL SWITCH CONSTRUCTION AND END PLUGTHEREFOR OR THE LIKE Primary Examiner-J. D. Miller AssistantExaminer-Fred E. Bell Attorney. Agent, or FirmCandor, Candor & Tassone[57] ABSTRACT An end plug for a switch construction, the plug having twoidentical inward and outward extensions extend ing from a large centralportion so as to be usable in a like manner regardless of whichextension is the inward or outward thereof in its assembled relationwith the switch casing whereby the inward extension is adapted toprovide a locating means for a spring inside the switch casing and theoutward extension is adapted to provide means for spacing an exposedpart of one of the switch conductors from the casing a predetermineddistance. Each of the extenions of the plug has an axial length at leastapproximately the same as the axial length of the central portionthereof. Each of the extensions of the plug of one embodiment has alocating means intermediate its ends whereby the locating means on theinward extension is adapted to provide locating means for positioningone end of the internal spring in the switch casing and the locatingmeans on the outward extension is adapted to provide means formechanically locking an adhesive thereto that secures the casing to theexposed portion of the conductor whereas in another embodiment each ofthe extensions of the plug has a smooth frusto-conical configuration.

10 Claims, 9 Drawing Figures ELECTRICAL SWITCH CONSTRUCTION AND END PLUGTHEREFOR OR THE LIKE RELATED APPLICATION This application is acontinuation-in-part application of its copending parent application,Ser. No. l63,l70, filed July 16, 197], now Pat. No. 3,778,742.

BACKGROUND OF THE INVENTION It is well known from applicatnts US. Pat.No. 3,519,972 that an insulating end plug can be provided for anelectrical switch casing for closing the same and for carrying one ofthe conductors of the electrical switch, such end plug having likeinward and outward extensions so as to be usable in a like mannerregardless of which extension is the inward or outward extension thereofin its assembled relation with the switch casing whereby an orientationproblem is eliminated in the automatic assembling of the end plug in theswitch casing.

SUMMARY This invention provides an improved switch construction of theabove type, as well as provides an improved end plug for such a switchconstruction or the like.

It has been found, according to the teachings of this invention, that ifthe large central portion of the end plug for the aforementioned switchconstruction is reduced in axial length while the axial length of eachof the extensions is increased even though the overall axial length ofthe plug remains the same, not only will it be easier to counterbore theswitch casing to receive the end plug of this invention, but also theexposed portion of the conductor passing through the plug of thisinvention will be spaced at predetermined distance from the outer casingby the plug extension with greater accuracy so as to meet all electricalcode requirements that were met in the past solely by extending theepoxy or adhesive means beyond the plug extension for this purpose.

It has been found, according to the teaching of this invention, that oneembodiment of the end plug for such a switch construction can beutilized for providing positive locating means for an internal spring ofthe switch construction and that such locating means can be provided onthe inward and outward extensions of the end plug in a like manner sothat the end plug can be usable in any assembled relation with theswitch casing. In this manner, the locating means that is provided onthe outward extension of the end plug will provide means to mechanicallylock the sealing adhesive utilized for securing the switch constructiontogether in a manner hereinafter set forth.

However, in another embodiment of the plug of this invention, each ofthe extensions can have a smooth frustoconical configuration as the endplug of U.S. Pat. No. 3,5l9,972.

Thus, the unique feature of having like extensions on the end plug stillremains a feature of this invention while having the additional featureof providing an improved end plug over the end plug disclosed in theaforementioned US. Pat. No. 3,5l9,972, to Merrill.

Accordingly. the switch construction of this invention has an open endedcasing provided with two conductors and means for normally maintainingone electrical relationship between the conductors and for providinganother electrical relationship between the conductors upon theoccurrence of a certain event. The switch construction has a rigidinsulating plug closing the open end of the casing and having a centralopening passing therethrough and through which one of the conductors isreceived so as to extend outwardly from the casing and inwardly into thecasing for its switching function. The plug has two identical inward andoutward extensions extending from a large central portion thereof so asto be usable in a like manner regardless of which extension is theinward or outward thereof in its assembled relation with the casingwhereby the inward extension provides a locating means for a springinside the casing and the outward extension provides means for spacingthe exposed part of the one conductor from the casing a predetermineddistance. Each of the extensions of the plug has an axial length atleast approximately the same as the axial length of the central portionof the plug. Each of the extensions of one embodiment of the plug has alocating means intermediate its ends, the locating means of the inwardextension providing positive locating means for positioning one end ofthe internal spring in the casing and the locating means on the outwardextension providing means for mechanically locking an adhesive theretothat secures the casing to the exposed portion of the conductorextending from the plug. Each of the extensions of another embodiment ofthe plug has a smooth frusto-conical configuration.

Accordingly, it is an object of this invention to provide an improvedswitch construction having one or more of the novel features of thisinvention as set forth above or hereinafter shwon or described.

Another object of this invention is to provide an improved end plug forsuch a switch construction or the like.

Other objects, uses and advantages of this invention are apparent from areading of this description which proceeds with reference to theaccompanying drawings showing a part thereof and wherein:

FIG. 1 is a longitudinal cross section of one embodiment of theinvention.

FIG. 2 is a cross-section of the insulating end plug of this inventionfor the switch construction of FIG. 1.

FIG. 3 is an elevation view of the relatively weak spring of the switchconstruction of FIG. 1.

FIG. 4 is a cross section of an electrically conductive slidable memberof the switch construction of FIG. 1.

FIG. 5 is a longitudinal cross section of another embodiment of theinvention.

FIG. 6 is an elevation of the completed switch of all the embodiments ofthis invention, the switch being drawn substantially to the same scaleand size as the actual switch construction.

FIG. 7 is a longitudinal cross section of the switch construction ofFIG. 1 with the bottom half of such view illustrating the end plug ofthis invention and the upper half of the view illustrating the end plugof US. Pat. No. 3,5l9,972.

FIG. 8 is a longitudinal cross-sectional view similar to FIG. 7 exceptthat the bottom half of such view illustrates another embodiment of theend plug of this invention.

FIG. 9 is a cross-section view of the end plug of the switchconstruction of FIG. 8.

Referring now to FIGS. 1-4, one embodiment of the switch construction ofthis invention is generally indicated by the reference numeral 10 andcomprises a cylindrical, tublular, electrically and thermally conductivecasing 12 having closures l4 and 16 at each end thereof. The closure orplug 16 is formed of electrically non-conductive material, such asceramic or the like.

A first conductor 18 conductively contacts the casing 12 at the integralclosure 14 therof. A second conductor 20 extends into the casing 12through the electrically non-conductive end closure or plug 16. Anormally solid fusible pellet 22 is spring-biased to exert outwardpressure against the closure 14.

An electrically conductive member 24 is slidably mounted within thecasing 12. The member 24 has a slidable, resilient, peripheralconductive engagement with the conductive casing 12 by the outwardlyextending resilient integral teeth 26 thereof which outwardly pressagainst the inner surface of the casing 12. The member 24 also has aconductive centeal portion 28 in conductive flow condition with thesecond electrical conductor 20 in one position of the member 24 and outof electrical flow condition with the second electrical conductor 20 inanother position of the member 24.

A compression spring construction outside of the pellet 22 is held undercompression between the member 24 and the casing 12 to change theelectrical flow condition between the casing 12 and the electricalconductor 20 upon collapse of the pellet 22 by leftward movement of theconductor member 24 away from the electrical contact with the conductor20.

The end closure or plug 16 has a central opening 30 passinglongitudinally therethrough and surrounding the second conductor 20. Theplug 16 is secured in the conductive casing 12 at the right casing endthereof by a large diameter, cylindrical, main body or central portion32 of the plug 16 engaging the inside surface 34' of the conductivecasing 12.

The plug 16 has two identical smaller diameter in ward and outward plugextensions 36 and 38 extending from opposite sides of the centralportion 32 thereof with the outward plug extension 38 extending out ofone end of the conductive casing 12 and with the inward extension 36extending into the conductive casing 12 and engaging a conductorarresting means. such as the conductor head means 40 at the inner end ofthe second conductor 20.

A sealing compound or adhesive means 42 surrounds a portion of theoutward plug extension 38, a portion of the second conductor 20 adjacentthe outward plug extension 38, and is sealed against the right-hand endofthe casing 12 at an inward flange 44 thereof, not only to secure theconductor 20 to the casing 12 but also to provide a non-conductivespacing between the casing 12 and the exposed portion of the conductor20 of at least a predetermined amount. Such inward flange 44 holds themain plug body 32 and the outward plug extension 38 from outwardmovement.

The identical plug extensions 36 and 38 have identical graduallydecreasing surface diameters as shown in FIGS. 1, 2 and and suchextensions also have flat transverse end surfaces 46 and 48 with theflat surface 46 engaging and holding the head means 40 of the conductorto prevent outward movement of the second conductor 20 out of the casing12 and plug 16.

The casing 12 has a thinner wall portion 34 or counterbore at the rightend of the conductive casing 12 with inward casing flanges 44 and 50 ateach end of the thin wall portion 34. The thin wall portion 34 holds themain body 32 of the plug 16 and the inward casing flanges 44 and 50 holdthe plug extensions 36 and 38 from longitudinal movement.

As illustrated in FIGS. 1, 2 and 5, the plug 16 of this invention haseach of the extensions 36 and 38 thereof defined by two frusto-conicalparts 35 and 37 joined together at the junction thereof by an outwardlydirected annular edge 39 which defines an outwardly directed locatingmeans of this invention on the particular extension 36 and 38 for apurpose hereinafter described. It can be seen that each annular locatingmeans 39 is arcuate in any axial cross section of the part 16.

The compression spring construction includes a relatively strongcompression spring 52 between the pellet 22 and the electricallyconductive member 24. Such compression spring construction also includesa relatively weak compression spring 54 between the plug 16 and theelectrically conductive member 24. As long as the pellet 22 does notcollapse, the strong spring 52 holds the slidable conductive member 24against the head 40 of the conductor 20 so that there is an electricalflow condition between the second conductor 20 in the casing 12, and,thus, to the first conductor 18. However, when the pellet 22 collapes,the material of such pellet 22 substantially instantaneously becomesfluid and flows around a disc means 56 and allows the strong spring 52to extend toward closure 14 so that its spring load becomes less thanthe spring load of the relatively weak spring 54. This permits such weakspring 54 to move the conductive member 24 away from the conductor head40 so that the conductor member 24 moves out of electrical flowcondition with respect to the second electrical conductor 20 and thisbreaks the electrical flow condition between the conductors 20 and 18 tostop the flow of current therethrough.

The disc means 56 is a spring load distributing disc, is of lessdiameter than the adjacent inner surface of casing 12 and is adjacentone end of the strong spring 52. The strong spring 52 may have anotherspring means distributing disc means 58 adjacent its other spring end.The disc means 58 is of less diameter than the adjacent inner surface ofcasing 12. In this manner, the disc means 56 and 58 distribute thespring load of spring 52 against the pellet 22 and against the centralpart 28 of slidable member 24. The discs 56 and 58 may be flat-sidedmetal or conductive discs and thus effectively distribute the springload.

The first electrical conductor 18 is secured to the integral conductiveend wall closure 14 by the flange means 60 and 62. The pellet 22 may beadjacent or near the integral conductive end wall 14 as illustrated.

The disc means 58 is adjacent one of the spring ends of the relativelyweak spring 54 but on the left side 28 of slidable member 24 anddistributes the spring load of such weak spring 54 by backing up thecentral portion 28 of the slidable member to prevent bulging of suchcentral portion 28 as may be seen in FIG. 1.

It can be seen that when the extension 36 of the plug 16 is disposedinside the casing 12 as illustrated in FIG. 1, the right-hand end 55 ofthe weak spring 54 nests against the locating means 39 of the extension36 so as to provide a positive location for the right-hand end 55 of thespring 54. In contrast, such right-hand end of the spring 55 would tendto slide up the smooth frustoconical plug extension of the plug of theaforementioned US. Pat. No. 3,519,972, and thus does not remainsubstantially cylindrical throughout its entire length in its assembledrelation in the switch construction 10.

When the epoxy resin or other adhesive means 42 is utilized to securethe casing I2 around the plug extension 38 and to an exposed portion ofthe conductor 20 as illustrated in FIG. 1, such epoxy or compound 42fills into the annular recesses defined by the locating means 39 on theoutward extension 38 as illustrated to mechanically lock such compound42 to the plug extension 38 when such compound hardens to therebyprovide greater surface area and locking between the compound 42 and theplug extension 38 than when the plug extension 38 is merely a straightand smooth frusto-conical extension as provided in the aforementionedU.S. Pat. No. 3,519,972.

Thus, the locating means 39 on the extensions 36 and 38 respectivelyprovide the dual function of locating the right-hand end 55 of thespring 54 as well as mechanically locking the compound 42 in placeregardless of which extension 36 or 38 extends into the casing I2 or outof the same whereby automatic machinery can still be utilized toassemble the end plug l6 into the easing 12 during the assemblingoperation of the switch construction of this invention.

In the operation of the embodiment of FIGS. 1-4, opposite power linesare connected espectively to conductors I8 and whereby the normalcondition respectively the switch I0 is as illustrated in FIG. 1 wherebyelectrical conductivity is provided between such conductors I8 and 20.The parts of the switch 10 remain in conductive condition and in theposition illustrated in FIG. 1 as long as the casing 12 remains at atemperature below the collapse temperature of the pellet 22. However,when the temperature adjacent the pellet 22 reaches the collapsetemperature, the pellet 22 collapses and becomes fluid or otherwisemovable past disc 56.

Thus, the left end of the strong spring 52 moves leftward enough toreduce its spring load below that of weak spring 54. This permits thespring 54 to move the movable member 24 leftwardly away from head 40 andthus break the electrical conductivity condition between the conductorsI8 and 20.

FIG. 5 shows another embodiment somewhat similar to the embodiment ofFIG. 1. However, the disc means 64 of FIG. 5 is placed adjacent theconductor head means 66 of the second conductor 68. Otherwise all of theparts of FIG. 5 are identical with the corresponding parts of FIG. 1 andtherefore such parts need not again be completely described inconnection with FIG. 5.

The head 66 in FIG. 5 has a substantially flat portion 70 with a roundededge 72. This permits the flat portion 70 to provide a relatively largesurface and good electrical conductivity between the second conductor68, disc means 64, slidable member 24 and the casing 12. At the sametime, the disc 64 provides substantially the same movement distributingcharacteristics as the disc 58 in FIG. I for both of the springs 52 and54.

The head 40 of FIG. I may be somewhat or almost continuously rounded toprovide a good conductive contact between the head 40 and the flatportion 28 of the slidable conductor member 24. The head 66 of FIG. 5 ismade of good electrical conductive metal and has an extensive flatsurface contact at the flat surface 70 with the flat sided goodconductor disc means 64. This provides a very good conductive contactbetween head 66 and slidable conductor member 24 which is better thanthe corresponding parts in FIG. I. The small rounded edges 72 of head 66are sufficient to prevent arcing when the head 66 and disc 64 areseparated. When the flat surfaces of head 66 are separated, such flatsurfaces therefore have greater interruption capacity because of suchflat surfaces and small rounded edges than corresponding parts of FIG.1.

Therefore, the embodiment of FIG. 5 has a better electrical conductivityand also has greater interruption capacity of resistive loads than theembodiment of FIG.

All of the other parts of FIG. 5 may be substantially the same instructure and function as the corresponding parts of FIG. 1 and it istherefore believed unnecessary to repeat the description thereof.

As previously stated, one of the advantages of the improved end plug ofthis invention over the end plug set forth in applicants U.S. Pat. No.3,519,972, is that the large central portion 32 of the end plug 16 ofthis invention is reduced in axial length over the axial length of thelike part thereof in the aforementioned United States patent while theaxial length of each of the extensions 36 and 38 of the end plug of thisinvention is increased even though the overall axial length of the plug16 remains the same not only for the purpose of making it easier tocounter-bore the thin walled portion 34 of the switch casing 12 in orderto receive and secure the end plug 16 of this invention in place, butalso to make sure, in a more accurate manner, that the exposed portionof the conductor 20 passing through the end plug 16 of this inventionwill be spaced a predetermined distance from the outer casing 12 at theflange 44 thereof by electrically insulating material so as to meet allelectrical code requirements for such spacing that were met in theelectrical switch construction of the aforementioned patent applicationsolely by making sure that the securing epoxy or adhesive means extendedbeyond the plug extension and along the conductor a certain amount forthis purpose.

This feature of this invention permits all of the other parts of theswitch construction of U.S. Pat. No. 3,5 l9,972, to have approximatelythe same dimensions to produce a switch construction that has an overallaxial length between the exposed parts of the opposed leads l8 and 20 ofapproximately 0.457 of an inch whereby it can be seen that the size ofthe casing 12 is relatively small and that in order to prevent shortcircuiting inside the casing 12 after the thermally responsive devicehas blown, the demensions of the casing 12 cannot be appreciably reducedand still have a functioning device. Thus, by merely changing the endplug and counterbore in the casing of such prior switch constructionaccording to the teachings of this invention all of the features andsizes of the prior switch construction are maintained while having theadded features as set forth above.

Thus, reference is now made to FIG. 7 wherein an axial cross-sectionalview of the prior art switch construction of applicants aforementionedU.S. patent is illustrated in the upper half thereof while the switchconstruction 10 of this invention as illustrated in FIG. I is providedin the bottom half of FIG. 7 in order to fully illustrate theaforementioned features whereby parts of the prior art switchconstruction similar to the parts of the switch construction 10 of thisinvention are indicated by like reference numerals and followed by thereference letter A.

As illustrated in FIG. 7, it can be seen that the central part 32 of theend plug 16 of this invention has its axial length reduced from theaxial length of the corresponding part 32A of the previously utilizedend plug 16A while the axial length of each of the extensions 36 and 38is increased over the axial length of the corresponding extension 36A or38A while the over-all length of the plug 16 of this invention remainsthe same as the over-all length of the prior plug 16A. In the embodimentof the end plug 16 of this invention, it can be seen that the axiallength of each of the extensions 36 and 38 of the end plug 16 of thisinvention have been increased to at least approximately the same axiallength as the axial length of the central portion 32 thereof.

For example, the overall length of the end plugs 16 and 16A isapproximately 0.219 of an inch when the switch body between the exposedportions of the leads l8 and 20 has the aforementioned axial length ofapproximately 0.457 of an inch. The central part 32A of the prior endplug 16A has an axial length of approximately 0. I of an inch and eachof the extensions 36A and 38A thereof has an axial length ofapproximately 0.057 of an inch whereas the central part 32 of the endplug 16 ofthis invention has an axial length of approximately 0.075 ofan inch and each of the extensions 36 and 38 thereof has an axial lengthof approximately 0.072 of an inch. the central parts 32 and 32A eachhaving the same diameter of approximately 0. M2 of an inch and eachextension 36, 38, 36A and 38A having a diameter at the free end thereofapproximately 0.075 to 0.088 of an inch.

With the central portion 32 of the end plug 16 having a smaller axiallength than the axial length of the corresponding parts 32A of the endplug 16A, the length of the counterbore in the casing 12 that forms thethin wall section 34' for receiving the central portion 32 issubstantially shorter than the corresponding counterbore 34'A in theprior switch casing 12A. Also, the overall length of the casing 12 isshorter than the casing 12A. Thus, the shorter counterbore 34' is easierand more economical to make than the larger counterbore 34'A,particularly when realizing the relatively small structure and partsthat are being formed to produce the switch construction as representedby substantial actual sizing in FIG. 6.

Further, from FIG. 7, it can be seen that the distance that theextension 38 of the end plug 16 provides from the casing flange 44 tothe exposed portion of the conductor 20 is a greater distance than thedistance provided between the flange 44A of the casing 12A and theexposed portion of the conductor 20A at the extension 38A of the endplug 16A so that the greater length provided by the extension 38 of theend plug 16 of this invention insures that the spacing between thecasing 12 and the conductor 20 will meet all of the electrical coderequirements. particularly when the epoxy or adhesive means 42 isdisposed in place as illustrated. For example, this spacing must beapproximately three millimeters and with the end plug 16 of thisinvention dimensioned as previously described, a straight line from apoint on the exposed portion of the end 44 of the casing 12 to a pointon the conductor 20 while passing through a point on the outer edge ofthe free end 48 of the extension 38 of the end plug 16 will beapproximately 3.22 millimeters or 0.l27 of an inch so that merely covering the extension 38 with the epoxy 42 will insure tht the threemillimeter spacing will be provided.

While the end plug 16 of this invention as previously described has theadvantage of the locating means 39 on the extensions 36 and 38 thereoffor the reasons pre viously described, it is to be understood that theunique features of a smaller counterbore in the casing 12 and theaccuracy in the spacing of he casing 12 from the exposed portion of theconductor 20 provided by the end plug 16 of this invention can still beprovided without the use of the locating means 39 on the extensions 36and 38 if desired.

Therefore, reference is now made to FIGS. 8 and 9 for another embodimentof this invention wherein it can be seen in FIG. 8 that the upper halfof the view illustrates the prior switch construction and the end plugtherefor as provided by applicants aforementioned US. patent andprovides in the lower half thereof another end plug 168 of thisinvention whereby parts thereof similar to the switch construction 10previously described are indicated by like reference numerals followedby the reference letter B.

As illustrated in FIGS. 8 and 9, it can be seen that the extensions 36Band 38B of the end plug 163 of this invention each has a smoothfrusto-conical configuration extending from the central portion 328thereof in much the same manner as the extensions 36A and 38A of theprior end plug 16A except that the length of the extensions 36B and 38Bare longer than the extensions 36A and 38A because of the reduced axiallength of the central portion 32B for the purposes previously described.

Thus, while the end plug 16B of this invention does not have thelocating means 39 of the end plug 16 previously described, the end plug16B of this invention does have the improved features over the priorknown end plug 16A for the reasons previously set forth in regards tothe description given in connection with FIG. 7 and as fully illustratedin FIG. 8, the diameters and axial lengths of the central part 328 andextensions 36B and 38B being the same lengths as previously set forthfor the end plug 16.

Thus, it can be seen that this invention not only provides an improvedswitch construction wherein the end closure or plug therefor can beinserted in place with either end extending into the casing and witheither end projecting out of the casing, but also this invention provides an improved end closure or plug for such a switch construction orthe like.

While the form of the invention now preferred has been illustrated anddescribed as required by the Patent Statutes, it is to be understoodthat other forms thereof may be utilized all coming within the scope ofthe appended claims.

What is claimed is:

I. In a switch construction having an open ended casing provided withtwo conductors and means for normally maintaining one electricalrelationship between said conductors and for providing anotherelectrical relationship between said conductors upon the occurrence ofacertain event, the switch construction having a rigid insulating plugclosing the open end of said casing and having a plug opening passingtherethrough and through which one of said conductors is received so asto extend outwardly from said casing and inwardly into said casing, saidplug having a large central portion secured to said casing, said plughaving two identical inward and outward extensions extending from saidcentral portion so as to be useable in a like manner regardless of whichextension is the inward or outward one thereof in its assembled relationwith said casing whereby the inward extension provides a locating meansfor a spring inside said casing and the outward extension provides meansfor spacing the exposed part of said one conductor from said casing apredetermined distance, the improvement wherein each of said extensionof said plug has an axial length at least approximately the same as theaxial length of said central portion of said plug.

2. In a switch construction as set forth in claim 1, the furtherimprovement wherein each of said extensions of said plug aresubstantially smooth frusto-conical parts.

3. In a switch construction as set forth in claim 1, the furtherimprovement wherein each of said extensions of said plug has an axiallength of approximately 0.072 of an inch and wherein said centralportion of said plug has an axial length of approximately 0.075 of aninch whereby the overall axial length of said plug is approximately0.2[9 of an inch.

4. In a switch construction as set forth in claim 3 the furtherimprovement wherein said central portion of said plug has a diameter ofapproximately 0.142 of an inch.

5. In a switch construction as set forth in claim 4 the furtherimprovement wherein each of said extensions of said plug at the free endthereof has a diameter of approximately 0.075 to 0.088 of an inch.

6. A plug for a switch construction having an open ended casing providedwith two conductors and means for normally maintaining one electricalrelationship between said conductors and for providing anotherelectrical relationship between said conductors upon the occurrence of acertain event, said plug comprising a rigid insulating member forclosing the open end of said casing and having a plug opening passingtherethrough and through which one of said conductors is adapted to bereceived so as to extend outwardly from said casing and inwardly intosaid casing, said plug having a large central portion adapted to besecured to said casing, said plug having two indentical inward andoutward extensions extending from said central portion so as to beuseable in a like manner regardless of which extension is the inward oroutward one thereof in its associated relation with said casing wherebythe inward extension is adapted to provide a locating means for a springinside said casing and the outward extension is adapted to provide meansfor spacing the exposed part of said one conductor from said casing apredetermined distance, each of said extensions of said plug having anaxial length at least approximately the same as the axial length of saidcentral portion of said plug.

7. A plug as set forth in claim 6 wherein each of said extensions ofsaid plug are substantially smooth frustoconical parts.

8. A plug as set forth in claim 6 wherein each of said extensions ofsaid plug has an axial length of approximately 0.072 of an inch andwherein said central portion of said plug has an axial length ofapproximately 0.075 of an inch whereby the overall axial length of saidplug is approximately 0.2 l9 of an inch.

9. A plug as set forth in claim 8 wherein said central portion of saidplug has a diameter of approximately 0.142 of an inch.

10. A plug as set forth in claim 9 wherein each of said extensions ofsaid plug at the free end thereof has a diameter of approximately 0.075to 0.088 of an inch.

1. In a switch construction having an open ended casing provided withtwo conductors and means for normally maintaining one electricalrelationship between said conductors and for providing anotherelectrical relationship between said conductors upon the occurrence of acertain event, the switch construction having a rigid insulating plugclosing the open end of said casing and having a plug opening passingtherethrough and through which one of said conductors is received so asto extend outwardly from said casing and inwardly into said casing, saidplug having a large central portion secured to said casing, said plughaving two identical inward and outward extensions extending from saidcentral portion so as to be useable in a like manner regardless of whichextension is the inward or outward one thereof in its assembled relationwith said casing whereby the inward extension provides a locating meansfor a spring inside said casing and the outward extension provides meansfor spacing the exposed part of said one conductor from said casing apredetermined distance, the improvement wherein each of said extensionof said plug has an axial length at least approximately the same as theaxial length of said central portion of said plug.
 2. In a switchconstruction as set forth in claim 1, the further improvement whereineach of said extensions of said plug are substantially smoothfrusto-conical parts.
 3. In a switch construction as set forth in claim1, the further improvement wherein each of said extensions of said plughas an axial length of approximately 0.072 of an inch and wherein saidcentral portion of said plug has an axial length of approximately 0.075of an inch whereby the overall axial length of said plug isapproximately 0.219 of an inch.
 4. In a switch construction as set forthin claim 3 the further improvement wherein said central portion of saidplug has a diameter of approximately 0.142 of an inch.
 5. In a switchconstruction as set forth in claim 4 the further improvement whereineach of said extensions of said plug at the free end thereof has adiameter of approximately 0.075 to 0.088 of an inch.
 6. A plug for aswitch construction having an open ended casing provided with twoconductors and means for normally maintaining one electricalrelationship between said conductors and for providing anotherelectrical relationship between said conductors upon the occurrence of acertain event, said plug comprising a rigid insulating member forclosing the open end of said casing and having a plug opening passingtherethrough and through which one of said conductors is adapted to bereceived so as to extend outwardly from said casing and inwardly intosaid casing, said plug having a large central portion adapted to besecured to said casing, said plug having two indentical inward andoutward extensions extending from said central portion so as to beuseable in a like manner regardless of which extension is the inward oroutward one thereof in its associated relation with said casing wherebythe inward extension is adapted to provide a locating means for a springinside said casing and the outward extension is adapted to provide meansfor spacing the exposed part of said one conductor from said casing apredetermined distance, each of said extensions of said plug having anaxial length at least approximately the same as the axial length of saidcentral portion of said plug.
 7. A plug as set forth in claim 6 whereineach of said extensions of said plug are substantially smoothfrusto-conical parts.
 8. A plug as set forth in claim 6 wherein each ofsaid extensions of said plug has an axial length of approximately 0.072of an inch and wherein said central portion of said plug has an axiallength of approximately 0.075 of an inch whereby the overall axiallength of said plug is approximately 0.219 of an inch.
 9. A plug as setforth in claim 8 wherein said central portion of said plug has adiameter of approximately 0.142 of an inch.
 10. A plug as set forth inclaim 9 wherein each of said extensions of said plug at the free endthereof has a diameter of approximately 0.075 to 0.088 of an inch.